The present invention relates to a process for the treatment of fresh meat, in particular for preserving fresh beef, pork, veal, lamb, game, poultry, horsemeat, fish, raw sausage and ham, in which the fresh meat is stored for a presettable time at a superatmospheric pressure in an air-tightly sealable space after supply of oxygen in an atmosphere essentially consisting of oxygen. The invention also relates to an apparatus for carrying out such a process.
In the various known processes for the treatment of fresh meat, attempts have already been made to expose the fresh meat to an oxygen atmosphere at elevated pressure in order in this manner to achieve the storage stability of the fresh meat and, in particular, to achieve a long-lasting fresh state which is expressed in an intense red meat color which is also to remain for a plurality of days in the open state of the meat. In a known process, here, the pressure built up was decreased and built up again several times over the storage period, whereas in a further known process, the pressure which was built up once remained over the entire storage period, but new oxygen was fed continuously and correspondingly old oxygen was removed from the space containing the fresh meat.
However, test results have shown that reliable improvement in the storage stability of the fresh meat cannot be achieved using the known processes. Firstly, in many cases the treated meat pieces, after they were re-exposed to the ambient atmosphere after completion of the oxygen treatment, developed gray spots after a relatively short time, which spots occurred particularly rapidly in particular at the contact points between two meat pieces. Secondly, the fresh meat pieces, after treatment had been carried out, were in many cases either frozen or swollen in a spongiform manner and beset with bubbles, so that in one case they can no longer be marketed in accordance with the food regulations as fresh meat and in the other case can no longer be marketed at all.
An object of the invention is to develop a process of the type mentioned at the outset in such a manner that the desired storage stability of the fresh meat is achieved and the intensive read meat color accompanying this is reliably and repeatably achieved in virtually 100 percent of all treatments.
This object is achieved, starting from a process of the type mentioned at the outset, according to the invention by means of the fact that, during the supply of the oxygen, its temperature is selected such that, and the feed rate is set or controlled to below enough that, the fresh meat does not freeze, that the pressure during the storage is selected to be high enough, and the storage time long enough, so that the fresh meat is completely penetrated by oxygen, and that, during the removal of the oxygen, the removal rate is set or controlled to be low enough that, firstly, the fresh meat does not freeze and, secondly, the oxygen permeating the treated fresh meat is removed from the fresh meat without bubble formation.
According to the invention it has been found that for a reliable and repeatable improvement in the storage stability of fresh meat it is necessary that the fresh meat must be completely, i.e. to its core, penetrated by oxygen. Only if the pressure at which the oxygen impinges on the outer surface of the fresh meat is selected high enough, and the storage time long enough, so that the fresh meat is completely penetrated by oxygen does the treated fresh meat remain, even after completion of the oxygen treatment, of constant quality for from 4 to 5 days, which is expressed by a constant intensive red meat color.
The intensive red meat color is achieved by means of the fact that virtually every cell of the meat is enriched with oxygen, the carbon dioxide formed in the cells after slaughter being displaced by oxygen. If even only a minimal region of the treated meat is not penetrated by oxygen, after completion of the treatment and removal of the pressure acting on the meat, the carbon dioxide present in the untreated region can extend through all of the remaining region of the treated fresh meat. The oxygen treatment is reversible in this case, so that after a relatively short time the carbon dioxide penetrates to the outside of the treated meat and green or gray spots form there due to oxidation.
Only if the fresh meat is completely penetrated by oxygen as far as the core does there result an irreversible process which ensures that the desired intensive red color is retained over a plurality of days in the open state of the meat.
A further, essential discovery of the invention is that freezing of the fresh meat is caused not only by too rapid a supply of the oxygen at the beginning of the treatment but also by too rapid a removal of the oxygen at the end of the treatment. According to the invention, not only is the oxygen supply rate, but also the oxygen removal rate, set or controlled to be low enough to prevent freezing of the fresh meat. If the preset supply rate is substantially exceeded, the fresh meat freezes even at the beginning of the treatment, so that during storage the oxygen cannot penetrate into the meat and the desired permeation with oxygen does not take place.
If the rate during the removal of the oxygen is set too high, two different effects can occur. Firstly, the fresh meat can also freeze in this case, which leads to the treated meat no longer being able to be termed fresh meat in accordance with food law provisions. Secondly, insufficient time is given to the oxygen which is present at high pressure in each cell of the treated fresh meat to diffuse out of the meat into the ambient atmosphere. In the event of too rapid a removal of the oxygen, this leads to the cells, on completion of the treatment, still being filled with oxygen at a pressure above the ambient pressure. In this case the meat has an expanded spongiform consistency, with in addition, bubble or froth formation being able to occur on the meat surface due to the overpressure present in the meat and the moisture present in the meat.
According to a further advantageous embodiment of the invention, during the storage of the fresh meat there is no supply and removal of oxygen. It has been found that such a supply and removal is unnecessary and the best and most reliable results are achieved when the meat, during the storage time, is exposed, completely sealed-off, to the pressure action of the oxygen present in the sealed space.
In addition, according to the invention, the fresh meat is preferably treated in sliced pieces, in particular in consumer portions. Since it is essential that the meat to be treated is completely permeated by oxygen as far as its core, and such a complete penetration can be achieved in practice only with difficulty in the case of unsliced large meat pieces, according to the invention preferably, sliced pieces are used. This ensures that at the preset parameters, such as pressure and treatment time, the meat pieces introduced into the space are completely penetrated by oxygen as far as their core.
According to a further preferred embodiment of the invention, during supply of the oxygen the pressure present within the sealed-off space is measured and, after a preset maximum pressure is reached, the oxygen supply is terminated. Preferably, the oxygen atmosphere in the sealed-off space in this case is brought to a pressure of approximately 10 to 10 bar, in particular approximately 13 to 17 bar, preferably approximately 15 bar, and maintained during the storage time. Whereas a pressure which is above a preset maximum pressure can pose technical problems, so that the housing of the sealable space and the door must be manufactured and secured in an appropriately stable and thus costly manner, in the case of a pressure below the preset maximum pressure, there is no assurance that the meat to be treated is completely penetrated by oxygen up to its core.
According to a further advantageous embodiment of the invention, during the supply of the oxygen the pressure is increased in an essentially linear manner, in particular in a plurality of steps, preferably between 10 and 20, in particular in approximately 15, steps. It has been found that in the case of a linear increase in pressure, in particular in a plurality of steps, a particularly reliable treatment result is achieved, at the same time, the risk of the meat freezing was reduced virtually to zero. However, it is also possible in principle to increase the pressure continuously. It is essential in all cases that during the pressure build-up an essentially constant throughput in liters is employed, i.e., that, per bar built up, essentially the same amount of oxygen is supplied. This can be ensured, for example, by using controllable valves.
Preferably, the oxygen is supplied within approximately 45 minutes to 4 hours, in particular within approximately 1 to 3 hours, preferably within 1 to 2 hours. Advantageously, this supply is performed continuously. Whereas in the case of relatively small plants, which have, for example, a volume of the order of magnitude of 100 liters, the oxygen can be supplied in approximately 1 hour, in the case of larger plants which can have a volume up to 50,000 liters or more, a longer supply time is to be used.
Advantageously, in the case of a space having a volume of approximately 100 liters, a maximum of approximately 70 liters of oxygen per minute is supplied, in particular a maximum of approximately 30 to 60 liters of oxygen per minute or less. In the case of a space having a volume of approximately 15,000 liters, preferably, a maximum of 2500 liters of oxygen per minute are supplied, advantageously a maximum of approximately 1400 liters of oxygen per minute, in particular a maximum of approximately 1200 liters of oxygen per minute or less. If these throughputs in liters are exceeded, the meat situated in the sealed space freezes, so that the treatment no longer leads to the desired result.
According to a further advantageous embodiment of the invention, the storage time is selected to be approximately 5 to 15 hours, in particular approximately 7 to 12 hours, preferably approximately 8 to 10 hours. In this case the storage time is selected advantageously, in the case of meat stored in advance to be shorter than in the case of freshly slaughtered meat. Compared with the known processes, the storage time is thus significantly reduced, as a result of which, firstly, the flexibility of the process, and secondly, the economic efficiency, are significantly increased. This reduction in the treatment time is due to the control according to the invention of the oxygen supply rate and oxygen removal rate and to the discovery that after complete penetration of the fresh meat with oxygen, further storage within the high-pressure oxygen is no longer required, since the treatment process has already become irreversible.
According to a further preferred embodiment of the invention, during removal of the oxygen the pressure is decreased essentially linearly, in particular in a plurality of steps, preferably between 10 and 20, in particular in approximately 15, steps. Preferably, during removal of the oxygen, essentially the same time, in particular approximately 8 to 20 minutes, preferably approximately 13 to 16 minutes, is provided per bar of pressure decrease. Like the pressure build-up, the pressure removal can in principle also be performed continuously, in which case, in turn, essentially the same amount of oxygen or oxygen mixture is removed per bar of pressure decrease.
Precisely when the oxygen is removed, monitored control is necessary, since in addition to the freezing effects the described frothing effects with bubble formation can occur. If the oxygen is removed in such a manner that the pressure removal is performed essentially linearly, these adverse effects can be avoided.
Preferably, after a preset minimum pressure is reached, this is removed at a higher gradient. The minimum pressure in this case is advantageously selected to be between 0.5 and 1.2 bar, in particularly approximately 0.7 bar.
If the minimum pressure is selected to be too high, for example 1.5 bar, when the pressure removal, gradient is increased, the meat freezes or froths from approximately 1 bar, even if the pressure removal, down to this pressure, was performed slowly enough. From the correct preset minimum pressure, an outlet valve limiting the oxygen removal can be opened virtually completely without the fresh meat freezing.
Preferably, the oxygen is removed in approximately 1 to 4 hours, in particular in approximately 3 hours. These, values which are increased in comparison with the known processes ensure that, firstly, the fresh meat does not freeze and, secondly, the oxygen present in the fresh meat cells is given sufficient time to escape from the meat without bubble formation and to remove the superatmospheric pressure present in the meat.
According to a further preferred embodiment of the invention, the oxygen is supplied to the sealed space without prior removal of the gas mixture corresponding to the, ambient atmosphere. The gas mixture present in the sealed space at ambient pressure at the start of the treatment is compressed by the oxygen introduced at high pressure and mixed with the introduced oxygen. At a sufficiently high purity of the oxygen introduced, which is, for example, at least 50%, in particular at least 90%, preferably at least 95%, the gas mixture present during storage in the space is ensured to have a sufficiently high oxygen content of at least 50%, in particular at least 90%, preferably at least 95%.
In principle, however, it is also possible that, prior to supplying the oxygen, the gas mixture corresponding to the ambient atmosphere present in the sealed space is removed as far as the generation of a preset reduced pressure. In this manners, on introduction of oxygen of a correspondingly high degree of purity, the gas mixture present within the sealed-off space during storage can have a still higher oxygen content.
Further advantageous embodiments of the invention and an apparatus for carrying out the process of the invention are specified in the subclaims.